1. Field of the Invention
The present invention relates to a control program, a controller, and a boiler system that are related to a boiler group including a plurality of boilers controlled in combustion at stepwise combustion positions.
2. Description of the Related Art
Conventionally, in the case of bringing a steam pressure or a hot water temperature close to a target value through combustion in a boiler group including a plurality of boilers, control has been conducted widely on the boilers by calculating the number of combustion-subject boilers and their combustion positions based on an increase/decrease in desired load, technologies on which combustion control are disclosed (see, for example, Japanese Patent Application Laid-Open Publication No. 2002-130602).
Further, as technologies for improving combustion efficiency and steam productivity are disclosed, those on the boilers capable of low combustion, intermediate combustion, and high combustion are disclosed (see, for example, Japanese Patent Application Laid-Open Publication No. 6-147402).
However, in the case of combustion control on a boiler group including a plurality of boilers capable of low combustion and high combustion, if the combustion efficiency during low combustion is higher than that during high combustion, high-efficiency operations can be performed by increasing the number of the combustion-subject boilers based on the low combustion; however, in the case of combustion control based on low combustion, the number of the boilers is decreased as the desired loads decrease, so that start-and-stop losses are liable to occur.
On the other hand, if the combustion efficiency during high combustion is higher than that during low combustion, high-efficiency operations can be performed by increasing the number of the combustion-subject boilers based on the high combustion; however, in the case of combustion control based on high combustion, if the desired loads increase, it is necessary to newly start combustion in the standby boilers, so that the desired load follow-up performance deteriorates due to a delay in response.
Taking into account such a situation, there are technological demands for improving both the combustion efficiency and the desired load follow-up performance in combustion control on a boiler group including a plurality of installed boilers in which combustion is performed at a plurality of stepwise combustion positions.